The invention relates to a track monitoring device in which respective interrogation devices are provided at the boundaries of successive track sections, which interrogation devices trigger an occupied signal or a release signal, respectively, for the track section lying in front of or behind the train, as viewed in the direction of travel thereof, on the basis of reception of data, respectively, coded in a response device at the front and at the back end of each train regularly travelling over the track section.
A device of this type is known from German AS No. 1,244,836, and which may utilize as the response devices, a permanent magnet, a radioactive compound or some other body reflecting or emitting a beam. Such response devices respectively contain a uniform information for all trains as to whether the head of a train or, respectively, the end of a train is present. Thus, based on the reception of a proper sequence of train head and train end data by an interrogation device, the occupation of a track section lying ahead and the orderly clearance or release of the track section lying behind a train can be determined at the boundary between two track sections.
However, it is necessary that care be taken in equipping trains whereby response devices are arranged at the train head or at the train end to insure that train end data is supplied in proper sequence. Obviously, an improper arrangement of the response devices would prevent the orderly operation of the system. Further, in the event a train changes its direction of travel, for example with a switch-back, the appropriate response devices must always be interchanged.